Gear assembly having noise-reduction structure and power take-off unit therewith

ABSTRACT

A noise-reduction structure for use with a meshing gear assembly includes a toothed disk that is supported on a first gear so as to be frictionally engaged therewith, but rotationally and radially movable relative thereto. The circumferential width of each tooth formed on the toothed disk is preferably larger than the circumferential width of each tooth formed on the first gear, and the outer diameter of the toothed disk can be larger than the outer diameter of the first gear. The first gear and the toothed disk mesh with a second gear such that as the second gear rotates, the toothed disk and the first gear also rotate. However, the toothed disk and the first gear rotate at different speeds because the difference in the number of teeth formed thereon. Because the teeth formed on the toothed disk have a larger circumferential thickness and a larger outer diameter than the teeth formed on the first gear, a tight meshing engagement with the second gear is provided. This tight meshing engagement, in combination with the frictional engagement of the toothed disk with the first gear, takes up backlash between the first gear and the second gear, thereby reducing the amount of noise that is generated during operation of the meshing gear assembly.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/341,446, filed Dec. 18, 2001, the disclosure of whichis incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] This invention relates in general to noise-reduction structuresfor use with meshing gear assemblies. In particularly, this inventionrelates to an improved noise-reduction structure for use with a meshinggear assembly in a power take-off unit.

[0003] Power take-off units are well known mechanical devices that arecommonly used in conjunction with sources of rotational energy, such asvehicle engines and transmissions, for selectively providing power toone or more rotatably driven accessories. For example, power take-offunits are commonly used in a variety of industrial and agriculturalvehicles for operating hydraulic pumps that, in turn, operatehydraulically driven accessories, such as plows, trash compactors,lifting mechanisms, winches, and the like. The power take-off unitprovides a relatively simple and inexpensive mechanism for supplyingrotational power from the vehicle engine to operate the rotatably drivenaccessory.

[0004] To accomplish this, a typical power take-off unit includes arigid housing having a mounting surface formed thereon. An opening isformed through a portion of the mounting surface of the power take-offhousing. An input gear is rotatably supported within the housing andincludes a portion that extends outwardly through the opening formedthrough the mounting surface. The mounting surface of the power take-offunit housing is adapted to be secured (typically by a plurality ofbolts) to a corresponding mounting surface formed on a case of atransmission provided on the vehicle. An opening is also formed througha portion of the mounting surface of the transmission case. When thepower take-off unit housing is secured to the transmission case, theportion of the input gear extends through the opening formed through thetransmission case into meshing engagement with one of the transmissiongears, typically a transmission gear that is driven by the vehicleengine. As a result, the input gear of the power take-of unit isrotatably driven whenever the vehicle engine is operated.

[0005] The power take-off unit typically further includes an output gearthat is rotatably supported within the housing. The output gear mesheswith the input gear such that the output gear is rotatably driven by theinput gear whenever the vehicle engine is operated. The output gear is,in turn, connected to an output shaft that is rotatably supported on thepower take-off housing. The output shaft extends outwardly from thehousing of the power take-off unit and is adapted to be connected to therotatably driven accessory. In some instances, the output gear isdirectly connected to the output shaft. In those instances, the outputshaft is rotatably driven by the output gear whenever the vehicle engineis operated. In other instances, however, the output gear is connectedthrough a clutch assembly to the output shaft. The clutch assembly isprovided within the power take-off housing for selectively connectingthe output gear to the output shaft and, therefore, permitting selectiveor intermittent operation of the rotatably driven accessory whenever thevehicle engine is operated.

[0006] When a typical power take-off unit is operated, it oftengenerates an undesirable amount of noise. Such noise usually resultsfrom the combination of torsional vibrations that are generated from thevehicle engine to the power take-off unit and backlash or looseness thattypically exists between the meshing gears contained within the powertake-off unit. It has been found that such torsional vibrations cancause the loosely meshing gears to rattle against one another as theyare rotatably driven during use. Although the generation of such noisedoes not usually adversely affect the operation of the power take-offunit, it can be quite bothersome to persons that are located in thevicinity. A variety of noise-reduction structures for meshing gearassemblies are known in the art. However, such known noise-reductionstructures have been found to be deficient for various reasons. Thus, itwould be desirable to provide an improved noise-reduction structure foruse with a meshing gear assembly in a power take-off unit.

SUMMARY OF THE INVENTION

[0007] This invention relates to an improved noise-reduction structurefor use with a meshing gear assembly. The noise-reduction structureincludes a toothed disk that is supported on a first gear, such as on aninput gear of a power take-off unit. The toothed disk is supported onthe first gear in such a manner as to be frictionally engaged therewith,but rotationally and radially movable relative thereto. Thecircumferential width of each tooth formed on the toothed disk ispreferably larger than the circumferential width of each tooth formed onthe first gear when measured at the operating pitch diameter thereof.Also, the outer diameter of the toothed disk can be larger than theouter diameter of the first gear. The first gear and the toothed diskmesh with a second gear, such as a transmission gear, such that as thesecond gear rotates, the toothed disk and the first gear also rotate.However, the toothed disk and the first gear rotate at different speedsbecause the difference in the number of teeth formed thereon. Becausethe teeth formed on the toothed disk have a larger circumferentialthickness and a larger outer diameter than the teeth formed on the firstgear, a tight meshing engagement with the second gear is provided. Thistight meshing engagement, in combination with the frictional engagementof the toothed disk with the first gear, takes up backlash between thefirst gear and the second gear, thereby reducing the amount of noisethat is generated during operation of the meshing gear assembly.

[0008] Various objects and advantages of this invention will becomeapparent to those skilled in the art from the following detaileddescription of the preferred embodiment, when read in light of theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is a sectional elevational view of a power take-off unitincluding a meshing gear assembly and a noise-reduction structure inaccordance with this invention.

[0010]FIG. 2 is an enlarged sectional elevational view of portions ofthe meshing gear assembly and the noise-reduction structure illustratedin FIG. 1.

[0011]FIG. 3 is a front elevational view of the meshing gear assemblyand the noise-reduction structure illustrated in FIGS. 1 and 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0012] Referring now to the drawings, there is illustrated in FIG. 1 apower take-off unit, indicated generally at 10, in accordance with thisinvention. The illustrated power take-off unit 10 is, in large measure,conventional in the art and is intended merely to illustrate oneenvironment in which this invention may be used. Thus, the scope of thisinvention is not intended to be limited for use with the specificstructure for the power take-off unit 10 illustrated in FIG. 1 or withpower take-off units in general. On the contrary, as will becomeapparent below, this invention may be used in any desired environmentfor the purposes described below.

[0013] The illustrated power take-off unit 10 includes a rigid hollowhousing 11 having a mounting surface 11 a formed thereon. An opening 11b is formed through the mounting surface 11 a for a purpose that will bedescribed below. An input gear 12 is rotatably supported in the housing11 of the power take-off unit 10. To accomplish this, an input shaft 13is journaled in a pair of aligned openings 13 a and 13 b formed throughthe housing 11 of the power take-off unit 10. Thus, the input shaft 13is stationary relative to the power take-off unit housing 11. The inputgear 12 is rotatably supported on the input shaft 13 by a pair ofbearings 14 and 15.

[0014] The input gear 12 has a first toothed gear portion 12 a and asecond toothed gear portion 12 b formed thereon. The first toothed gearportion 12 a is relatively large in diameter. As shown in FIG. 1, aportion of the first toothed gear portion 12 a extends through theopening 11 b formed through the mounting surface 11 a of the powertakeoff housing 11. Thus, when the power take-off unit 10 is mounted ona vehicle transmission (not shown) or other source of rotational powerin the manner described above, the first toothed gear portion 12 a ofthe input gear 12 extends through the opening 11 b into meshingengagement with one of the transmission gears, typically a transmissiongear that is rotatably driven whenever the vehicle engine is operated.As a result, the input gear 11 of the power take-of unit 10 is rotatablydriven whenever the vehicle engine is operated.

[0015] The power take-off unit 10 further includes an output gear,indicated generally at 20, that is rotatably driven by the input gear12. The output gear 20 is formed from a single, integral piece ofmaterial, including a toothed gear portion 20 a and a bell portion 20 b.The toothed gear portion 20 a of the output gear 20 meshes with thesecond toothed gear portion 12 b of the input gear 12. Thus, the outputgear 20 is rotatably driven by the input gear 12 whenever the vehicleengine is operated. The bell portion 20 b of the output gear 20 isgenerally hollow and cylindrical in shape and extends axially from thetoothed gear portion 20 a. The bell portion 20 b has a plurality ofslots 21 formed therein for a purpose that will be explained below.

[0016] The output gear 20 is rotatably supported in the housing 11 ofthe power takeoff unit 10. To accomplish this, an output shaft 22 isrotatably supported in a pair of aligned bearings 23 and 24. The bearing23 is journaled in a recess 23 a formed in the interior of the housing11 of the power take-off unit 10. The bearing 24 is journaled in arecess 24 a formed in a bearing cap 25 secured to the housing 11 of thepower takeoff unit 10. Thus, the output shaft 22 is rotatably supportedin the housing 11 of the power take-off unit 10. The output gear 20 isrotatably supported on the output shaft 22 by a bearing 26. The end ofthe output shaft 22 rotatably supported by the bearing 24 has aninternal spline 22 a, a key, or other similar structure formed thereinto facilitate the connection thereof to a rotatably driven accessory(not shown).

[0017] The power take-off unit 10 also includes a clutch assembly,indicated generally at 30, for selectively providing a drivingconnection between the bell portion 20 b of the output gear 20 and theoutput shaft 22. The clutch assembly 30 includes a first plurality offlat, annular clutch plates 31 that are connected to the bell portion 20b of the output gear 20 for rotation therewith. To accomplish this, eachof the first plurality of clutch plates 31 has one or more radiallyoutwardly extending protrusions formed thereon. The protrusions of theclutch plates 31 are received in the slots 21 formed in the bell portion20 b of the output gear 20 for rotation therewith. Thus, the firstplurality of clutch plates 31 are rotatably driven by the output gear 20whenever the vehicle engine is operated. The clutch assembly 30 furtherincludes a second plurality of flat, annular clutch plates 32. Thesecond plurality of clutch plates 32 is disposed in alternating fashionbetween the first plurality of clutch plates 31. The second plurality ofclutch plates 32 are splined to a clutch gear 33 that, in turn, issplined onto the output shaft 22. Thus, the second plurality of clutchplates 32, the clutch gear 33, and the output shaft 22 are connected forrotation together as a unit. The clutch gear 33 is restrained from axialmovement in one direction (toward the right when viewing FIG. 1) byabutment with the toothed gear portion 20 a of the output gear 20.

[0018] The clutch assembly 30 further includes an annular clutch piston34 that is disposed within a hollow cylindrical clutch cylinder 35. Theclutch cylinder 35 has a closed end and an opened end. One end of theclutch piston 34 (the left end when viewing FIG. 1) is disposed withinthe clutch cylinder 35, while the opposite end of the clutch piston 34(the right end when viewing FIG. 1) extends from the opened end of theclutch cylinder 35 adjacent to the first and second pluralities ofclutch plates 31 and 32. Both the clutch piston 34 and the clutchcylinder 35 are supported on the output shaft 22. The clutch piston 34is axially movable along the output shaft 34, but the clutch cylinder 35is restrained from axial movement in one direction (toward the left whenviewing FIG. 1) by one or more retaining rings 36 mounted on the outputshaft 22. A coiled clutch spring 37 reacts between the clutch piston 34and the clutch gear 33. As discussed above, the clutch gear 33 isrestrained from axial movement in one direction (toward the right whenviewing FIG. 1) by the toothed gear portion 20 a of the output gear 20.Thus, the clutch spring 37 urges the clutch piston 34 axially in theopposite direction (toward the left when viewing FIG. 1) toward adisengaged position adjacent to the closed end of the clutch cylinder35. In the disengaged position, the clutch piston 34 does not engage thefirst and second pluralities of clutch plates 31 and 32. Thus, theclutch plates 31 and 32 do not frictionally engage one another. As aresult, the clutch gear 33 is disconnected from the output gear 20 so asto provide no rotatable driving connection therebetween. In thiscondition, the output shaft 22 is not rotatably driven by the outputgear 20.

[0019] An annular clutch chamber 38 is defined between the clutch piston34 and the closed end of the clutch cylinder 35. This annular clutchchamber 38 communicates through a first transverse passageway 22 b andan axial passageway 22 c formed through the output shaft 22 with asource of pressurized fluid (not shown). As is well known, whenpressurized fluid is provided from the source to the annular clutchchamber 38, the clutch piston 34 is moved axially against the urging ofthe clutch spring 37 from the disengaged position to an engagedposition. In the engaged position, the clutch piston 34 compresses thefirst and second pluralities of clutch plates 31 and 32 together intofrictional engagement. As a result, the clutch gear 33 is connected tothe output gear 20 so as to provide a rotatable driving connectiontherebetween. In this condition, the output shaft 22 is rotatably drivenby the output gear 20.

[0020] The illustrated power take-off assembly 10 further includes anoise-reduction structure, indicated generally at 40, in accordance withthis invention. The structure of the noise-reduction structure 40 isillustrated in detail in FIGS. 2 and 3. As shown therein, thenoise-reduction structure 40 includes a toothed disk, generallyindicated at 41, that is retained on the first toothed gear portion 12 aof the input gear 12. The toothed disk 41 can be retained on the firsttoothed gear portion 12 a of the input gear 12 in any desired manner.For example, as shown in FIG. 2, the toothed disk 41 can be retained onthe first toothed gear portion 12 a of the input gear 12 by a retainingring 42. The retaining ring 42 is secured to the first toothed gearportion 12 a of the input gear 12 such that the toothed disk 41 isdisposed therebetween. The retaining ring 42 can be secured to the firsttoothed gear portion 12 a of the input gear 12 in any suitable fashion.For example, the retaining ring 42 can be secured to the first toothedgear portion 12 a of the input gear 12 by one or more countersunk capscrews 43. Four circumferentially spaced countersunk cap screws 43 areshown in FIG. 3. The retaining ring 42 and the cap screws 43 hold thetoothed disk 41 in frictional engagement with an axial face 44 of thefirst toothed gear portion 12 a of the input gear 12, but allow thetoothed disk 41 to be rotated relative to the first toothed gear portion12 a of the input gear 12. Additionally, the toothed disk 41 issupported in such a manner that it can move radially relative to thefirst toothed gear portion 12 a of the input gear 12, as will becomediscussed further below.

[0021] As shown in FIG. 3, the illustrated toothed disk 41 of thenoise-reduction structure 40 is annular in shape. The toothed disk 41has an outer circumferential portion 45 and an inner circumferentialportion 46. A plurality of teeth 47 (see FIG. 3) are formed on the outercircumferential portion 45 of the toothed disk 41. The first toothedgear portion 12 a of the input gear 12 likewise has an outercircumferential portion 48. A plurality of teeth 49 are formed on theouter circumferential portion 48 of the first toothed gear portion 12 aof the input gear 12. The number of teeth 47 formed on the outercircumferential portion 45 of the toothed disk 41 is different from thenumber of teeth 49 formed on the outer circumferential portion 48 of thefirst toothed gear portion 12 a of the input gear 12. Preferably, thenumber of teeth 47 formed on the outer circumferential portion 45 of thetoothed disk 41 exceeds the number of teeth 49 formed on the outercircumferential portion 48 of the first toothed gear portion 12 a of theinput gear 12 by one gear tooth, as illustrated in FIG. 3.

[0022] In a preferred embodiment of the invention, the teeth 47 formedon the outer circumferential portion 45 of the toothed disk 41 have alarger circumferential thickness than the teeth 49 formed on the outercircumferential portion 48 of the first toothed gear portion 12 a of theinput gear 12 at the operating pitch diameter D1 of the first toothedgear portion 12 a of the input gear 12. In other words, when measured atthe operating pitch diameter D1 of the first toothed gear portion 12 aof the input gear 12, the circumferential width of each tooth 47 formedon the toothed disk 41 is preferably larger than the circumferentialwidth of each tooth 49 formed on the first toothed gear portion 12 a ofthe input gear 12. This relationship between the relative sizes of theteeth 47 and the teeth 49 is shown in FIG. 3. Also, the outercircumferential portion 45 of the toothed disk 41 can have a diameter D2that is larger than a diameter D3 of the outer circumferential portion48 of the first toothed gear portion 12 a of the input gear 12. In otherwords, the outer diameter D2 of the toothed disk 41 can be larger thanthe outer diameter of the first toothed gear portion 12 a of the inputgear 12. The purpose of the larger circumferential thickness of theteeth 47 formed on the outer circumferential portion 45 of the tootheddisk 41 and the larger diameter of the outer circumferential portion 45of the toothed disk 41 will be explained below.

[0023] As shown in FIG. 2, the inner circumferential portion 46 of thetoothed disk 41 is preferably axially offset relative to the outercircumferential portion 45 of the toothed disk 41 by a taperedintermediate portion 46 a. Thus, the inner circumferential portion 46 ofthe toothed disk 41 is recessed within a recessed web portion 50 formedin the first toothed gear portion 12 a of the input gear 12. The innercircumferential portion 46 of the toothed disk 41 is somewhat flexiblerelative to the outer circumferential portion 45 of the toothed disk 41,similar to a Belleville spring. The inner circumferential portion 46 ofthe toothed disk 41 is preferably engaged by the retaining ring 42 thatis secured to the first toothed gear portion 12 a of the input gear 12.The inner circumferential portion 46 of the toothed disk 41 has a boreformed therethrough that defines an inner circumferential surface 51.The inner circumferential surface 51 defined by the bore has a diameterthat is larger than an outer diameter of a hub portion 52 of the firsttoothed gear portion 12 a of the input gear 12. This provides a radialclearance, as indicated at 53 in FIG. 2, between the innercircumferential portion 46 of the toothed disk 41 and the hub 52 of thefirst toothed gear portion 12 a of the input gear 12. The radialclearance 53 between the inner circumferential portion 46 of the tootheddisk 41 and the hub 52 of the first toothed gear portion 12 a of theinput gear 12 permits the toothed disk 41 to be supported in such amanner that it can move radially (e.g., in either direction of thearrows R shown in FIG. 2) relative to the first toothed gear portion 12a of the input gear 12. The diameter of the inner circumferentialsurface 51 defined by the bore through the inner circumferential portion46 of the toothed disk 41 is large enough so that radial movement of thetoothed disk 41 is sufficiently unencumbered by the countersunk capscrews 43 that secure the retaining ring 42 to the first toothed gearportion 12 a of the input gear 12.

[0024] In operation, the inner circumferential portion 46 of the tootheddisk 41 is somewhat flexible, as stated above. The toothed disk 41 issecured to the first toothed gear portion 12 a of the input gear 12 bythe retaining ring 42 so that the outer circumferential portion 45 ofthe toothed gear 41 frictionally engages the axial face 44 of the firsttoothed gear portion 12 a of the input gear 12. The first toothed gearportion 12 a of the input gear 12 and the toothed disk 41 securedthereto mesh with a transmission gear (not shown) in the mannerdescribed above. As the transmission gear rotates, the toothed disk 41and the input gear 12 rotate. However, the toothed disk 41 and the inputgear 12 rotate at different speeds because the number of teeth 47 formedon the outer circumferential portion 45 of the toothed disk 41 isdifferent from the number of teeth 49 formed on the outercircumferential portion 48 of the first toothed gear portion 12 a of theinput gear 12. As mentioned above, in the preferred embodiment of theinvention, the number of teeth 47 formed on the outer circumferentialportion 45 of the toothed disk 41 exceeds the number of teeth 49 formedon the outer circumferential portion 48 of the first toothed gearportion 12 a of the input gear 12 by one tooth. Consequently, thetoothed disk 41 will rotate faster that the input gear 12.

[0025] As stated above, the teeth 47 formed on the outer circumferentialportion 45 of the toothed disk 41 have a larger circumferentialthickness than the teeth 49 formed on the outer circumferential portion48 of the first toothed gear portion 12 a of the input gear 12 at theoperating pitch diameter D1 of the first toothed gear portion 12 a ofthe input gear 12. As a result, the toothed disk 41 meshes tighter withthe transmission gear than the first toothed gear portion 12 a of theinput gear 12. This tighter meshing engagement is further producedbecause the outer circumferential portion 45 of the toothed disk 41 hasa larger diameter D2 than the diameter D3 of the outer circumferentialportion 48 of the first toothed gear portion 12 a of the input gear 12.This tighter meshing engagement, in combination with the frictionalengagement of the toothed disk 41 with the input gear 12, takes upbacklash between the first toothed gear portion 12 a of the input gear12 and the transmission gear.

[0026] It should be appreciated by one of ordinary skill in the art thatthe tooth disk 41 according to the invention may be retained on theoutput gear 20, such as on the toothed gear portion 20 a of the outputgear 20. It should further be appreciated that the scope of theinvention is not intended to be limited to the input gear 12 or outputgear 20 shown and described but can be retained on other working gearsas well. Moreover, a noise-reduction gear assembly structure formed by aworking gear (i.e., the input gear 12 and the output gear 20illustrated) and toothed disk 41 according to the invention are notintended to be limited for use with the power take-off unit 10illustrated but can be used to reduce noise of any pair of meshinggears.

[0027] In accordance with the provisions of the patent statutes, theprinciple and mode of operation of this invention have been explainedand illustrated in its preferred embodiment. However, it must beunderstood that this invention may be practiced otherwise than asspecifically explained and illustrated without departing from its spiritor scope.

What is claimed is:
 1. A meshing gear assembly comprising: a first gearhaving a plurality of first gear teeth provided thereon; a toothed diskretained on said first gear so as to be frictionally engaged with saidfirst gear and rotationally and radially movable relative thereto, saidtoothed disk having a plurality of toothed disk teeth provided thereon;and a second gear having a plurality of second gear teeth providedthereon, said plurality of second gear teeth meshing with both saidplurality of first gear teeth and said plurality of toothed disk teeth.2. The meshing gear assembly defined in claim 1 wherein a portion ofsaid toothed disk is disposed about a portion of said first gear with aradial clearance therebetween.
 3. The meshing gear assembly defined inclaim 1 wherein said first gear includes a portion that defines an outerdimension and said toothed disk includes a portion that defines an innersurface that defines an inner dimension, and wherein said innerdimension defined by said portion of said toothed disk is larger thansaid outer dimension defined by said portion of said first gear.
 4. Themeshing gear assembly defined in claim 1 wherein said first gearincludes a hub having an outer circumferential surface that defines anouter diameter and said toothed disk includes an inner circumferentialsurface that defines an inner diameter, and wherein said inner diameterdefined by said inner circumferential surface of said toothed disk islarger than said outer diameter defined by said outer circumferentialsurface of said first gear.
 5. The meshing gear assembly defined inclaim 1 wherein each of the plurality of toothed disk teeth defines acircumferential width and each of the plurality of first gear teethdefines a circumferential width, and wherein the circumferential widthsdefined by each of the plurality of toothed disk teeth are greater thanthe circumferential widths defined by each of the plurality of firstgear teeth.
 6. The meshing gear assembly defined in claim 1 wherein saidplurality of toothed disk teeth define an outer diameter and saidplurality of first gear teeth define an outer diameter, and wherein theouter diameter defined by said plurality of toothed disk teeth is largerthan said outer diameter defined by said plurality of first gear teeth.7. The meshing gear assembly defined in claim 1 wherein (1) each of theplurality of toothed disk teeth defines a circumferential width, andsaid plurality of toothed disk teeth define an outer diameter, (2) eachof the plurality of first gear teeth defines a circumferential width,and said plurality of first gear teeth define an outer diameter, and (3)the circumferential widths defined by each of the plurality of tootheddisk teeth are greater than the circumferential widths defined by eachof the plurality of first gear teeth, and the outer diameter defined bysaid plurality of toothed disk teeth is larger than said outer diameterdefined by said plurality of first gear teeth.
 8. The meshing gearassembly defined in claim 1 further including a retainer ring that issecured to said first gear and retains said toothed disk on said firstgear.
 9. The meshing gear assembly defined in claim 8 wherein saidtoothed disk includes an inner circumferential portion that is flexiblerelative to an outer circumferential portion thereof, and wherein saidretaining ring engages said inner circumferential portion to retainersaid toothed disk on said first gear.
 10. The meshing gear assemblydefined in claim 9 wherein a tapered intermediate portion extendsbetween said inner circumferential portion and said outercircumferential portion of said toothed disk.
 11. A power take-off unitthat is adapted to connect a gear that is rotatably driven by a sourceof rotational energy to a driven accessory comprising: a hollow housing;an input gear supported within said housing, said input gear having aplurality of input gear teeth provided thereon; a toothed disk retainedon said input gear so as to be frictionally engaged with said input gearand rotationally and radially movable relative thereto, said tootheddisk having a plurality of toothed disk teeth provided thereon, saidinput gear and said toothed disk adapted to be rotatably driven by therotatably driven gear; and an output shaft supported within said housingand rotatably driven by said input gear, said output shaft adapted to beconnected to rotatably drive the driven accessory.
 12. The powertake-off unit defined in claim 11 wherein a portion of said toothed diskis disposed about a portion of said input gear with a radial clearancetherebetween.
 13. The power take-off unit defined in claim 11 whereinsaid input gear includes a portion that defines an outer dimension andsaid toothed disk includes a portion that defines an inner surface thatdefines an inner dimension, and wherein said inner dimension defined bysaid portion of said toothed disk is larger than said outer dimensiondefined by said portion of said input gear.
 14. The power take-off unitdefined in claim 11 wherein said input gear includes a hub having anouter circumferential surface that defines an outer diameter and saidtoothed disk includes an inner circumferential surface that defines aninner diameter, and wherein said inner diameter defined by said innercircumferential surface of said toothed disk is larger than said outerdiameter defined by said outer circumferential surface of said inputgear.
 15. The power take-off unit defined in claim 11 wherein each ofthe plurality of toothed disk teeth defines a circumferential width andeach of the plurality of input gear teeth defines a circumferentialwidth, and wherein the circumferential widths defined by each of theplurality of toothed disk teeth are greater than the circumferentialwidths defined by each of the plurality of input gear teeth.
 16. Thepower take-off unit defined in claim 11 wherein said plurality oftoothed disk teeth define an outer diameter and said plurality of inputgear teeth define an outer diameter, and wherein the outer diameterdefined by said plurality of toothed disk teeth is larger than saidouter diameter defined by said plurality of input gear teeth.
 17. Thepower take-off unit defined in claim 11 wherein (1) each of theplurality of toothed disk teeth defines a circumferential width, andsaid plurality of toothed disk teeth define an outer diameter, (2) eachof the plurality of input gear teeth defines a circumferential width,and said plurality of input gear teeth define an outer diameter, and (3)the circumferential widths defined by each of the plurality of tootheddisk teeth are greater than the circumferential widths defined by eachof the plurality of input gear teeth, and the outer diameter defined bysaid plurality of toothed disk teeth is larger than said outer diameterdefined by said plurality of input gear teeth.
 18. The power take-offunit defined in claim 11 further including a retainer ring that issecured to said input gear and retains said toothed disk on said inputgear.
 19. The power take-off unit defined in claim 18 wherein saidtoothed disk includes an inner circumferential portion that is flexiblerelative to an outer circumferential portion thereof, and wherein saidretaining ring engages said inner circumferential portion to retainersaid toothed disk on said input gear.
 20. The power take-off unitdefined in claim 19 wherein a tapered intermediate portion extendsbetween said inner circumferential portion and said outercircumferential portion of said toothed disk.